430 FISH AND BLUBBER OILS with 200 c.c. of Halphen's reagent (28 vols. of glacial acetic acid, 4 vols. of nitrobenzene and i vol. of bromine) : a yellow precipitate of bromo- compounds is obtained. After an hour's rest, the liquid is filtered off by means of a pump and the precipitate washed with cold ether, powdered and boiled for half an hour in a reflux apparatus with benzene (50 c.c. of benzene per gram of precipitate) : the octabromo-compounds of the fatty acids of marine animal oils remain undissolved by boiling benzene. The liquid is filtered through a steam-heated filter and the precipitate insoluble in benzene washed with boiling benzene, dried, and a determination made of its melting point, which should be above 190° (with incipient decom- position and blackening). If the melting point is below 190°, the precipitate is taken up several times with boiling benzene until a portion boiling above this temperature is obtained. A reaction similar to the above is given also by the drying oils—linseed, walnut and hempseed oils (see Linseed Oil) ; the hexabromo-compounds fur- nished by these oils are, however, soluble in boiling benzene and melt at 175- 180° without decomposing. According to Marcusson, the octabromo-compouncl test—which is often made on the fatty acids and not on the oil as such—is able to detect 10 % of marine animal oil mixed with linseed or other oil. (b) TORTELLI AND jAFFE's REACTION. In a graduated glass cylinder with a ground stopper, I c.c. of the oil, 6 c.c. of chloroform and i c.c. of glacial acetic acid are shaken together and 40 drops of a 10% solution of bromine in chloroform added ; the cylinder is again shaken vigorously for a moment and then placed on a white paper and the colour of the liquid observed. Marine animal oils in general give a green coloration with a yellowish or blue reflexion, which increases during the space of half an hour and afterwards changes to brown. With vegetable or terrestrial animal oils and fats, pale yellow or yellowish colorations are obtained, these grad- ually darkening for an hour and then changing to brown. For the reaction to succeed, the, oil and the reagents must be perfectly dehydrated and the vessels very dry. If the oil is highly coloured, it may be decolorised with sulphuric acid1 or soda.2 FISH AND BLUBBER OILS Fish oils proper are those obtained from the residues left during the preparation of various fish (sardines, herrings, shad, tunnyfish, etc.). From cetaceans are obtained mainly Whale oil and Seal oil, dolphin oil and por- poise oil being less common. In general these oils are liquid and often they are turbid and contain more or less abundant solid deposits; they 1 50 c.c. of the oil are treated for 5-6 hours, with occasional shaking, with 0-5 gram of cone, sulphuric acid and then filtered through a thin layer of fuller's earth ; the filtrate is washed with boiling water to render it free from acid and filtered through paper in an oven at 100°. 2 100 c.c. of the oil and 5 c.c. of 30% caustic soda solution are heated on the water- bath for a quarter of an hour with frequent shaking, 50-60 c.c. of saturated sodium chloride solution being then added and the heating on the water-bath continued for three-quarters of an hour, with shaking. The oil is then decanted off, washed two or three times with hot water and filtered in an oven at 100°.